Determining enclosure breach ultrasonically

Abstract

A structure intrusion may be determined. For example, a signal may be received corresponding to a wave propagating in the structure. Next, the received signal may be analyzed. Based on the analysis in a “passive mode”, a breach may be determined to have occurred in the structure when the received signal indicates that at least one aspect of the received signal crosses a predetermined threshold. Furthermore, based on the analysis in an “active mode”, a breach may be determined to have occurred in the structure when comparing the received signal to a baseline waveform indicates that at least one aspect of the received signal varies from the baseline waveform by a predetermined amount. The wave propagating in the structure may comprise an elastic wave and may be in an acoustic frequency range or in an ultrasonic frequency range.

What is claimed is: 
     
       1. A method for determining a structure intrusion, the method comprising:
 receiving, in a passive detection mode, a signal corresponding to an elastic wave propagating in the structure; 
 analyzing, by a processing device, the received signal; 
 determining that at least one aspect of the received signal crosses a predetermined threshold; and 
 switching from the passive detection mode to an active detection mode in response to a determination that at least one aspect of the received signal crosses the predetermined threshold, wherein switching from the passive detection mode to the active detection mode comprises switching from independent sensor operation to transmit-receive paired sensor operation. 
 
     
     
       2. The method of  claim 1 , wherein receiving the signal corresponding to the wave propagating in the structure comprises receiving the signal that interacted with at least one of the following: boundaries of the structure and variations of the structure. 
     
     
       3. The method of  claim 1 , wherein receiving the signal corresponding to the wave comprises receiving the signal corresponding to the wave comprising one of the following: the wave being an elastic wave in an acoustic frequency range and the wave being an elastic wave in an ultrasonic frequency range. 
     
     
       4. The method of  claim 1 , wherein analyzing the received signal comprises analyzing the received signal in a frequency domain. 
     
     
       5. The method of  claim 1 , wherein analyzing the received signal comprises analyzing the received signal in a frequency domain in terms of ratios of energies in different frequency bands. 
     
     
       6. The method of  claim 1 , wherein analyzing the received signal comprises analyzing the received signal in a time domain. 
     
     
       7. The method of  claim 1 , wherein analyzing the received signal comprises analyzing the received signal in a time-frequency domain. 
     
     
       8. A method for determining a structure intrusion, the method comprising:
 receiving, at a first state independent sensor operation mode, a first signal corresponding to a first wave propagating in the structure; 
 analyzing the received first signal; 
 determining that at least one aspect of the received first signal crosses a predetermined threshold; 
 switching, in response to a determination that the at least one aspect of the received first signal crosses the predetermined threshold, to a transmit-receive paired sensor operation mode second state; 
 receiving, at the paired sensor operation mode second state, a second signal corresponding to a second wave propagating in the structure; 
 analyzing, by a processor device, the received second signal; and 
 determining, in response to analyzing the received second signal, that a breach has occurred in the structure.